Fix GitHub Pages deploy job: artifact expiry on re-run

[Copilot]

The dynamic pages-build-deployment workflow's deploy job was being re-triggered days after the build job completed, by which point the github-pages artifact (1-day default retention) had expired — causing deploy to fail with Found 0 artifact(s).

Changes

• Added .github/workflows/pages.yml: Custom Pages deployment workflow that replaces reliance on the auto-generated dynamic workflow
  • deploy uses needs: build, ensuring it always runs immediately after build in the same workflow invocation — the artifact is guaranteed to exist
  • Triggered on push to master and workflow_dispatch
  • Proper pages: write + id-token: write permissions and concurrency guard to prevent parallel deployments

jobs:
  build:
    steps:
      - uses: actions/checkout@v5
      - uses: actions/configure-pages@v5
      - uses: actions/jekyll-build-pages@v1
      - uses: actions/upload-pages-artifact@v3

  deploy:
    needs: build          # <-- artifact always fresh; never a stale re-run gap
    environment:
      name: github-pages
    steps:
      - uses: actions/deploy-pages@v5